1. Field of the Invention
The present invention relates to a power control method and a power control system for polarity inversion in an LCD panel, and more particularly, to a power control method and a power control system for line inversion in an LCD panel.
2. Description of the Related Art
LCD (Liquid Crystal Display) panels are widely used in PDAs (Personal Digital Assistants), mobile phones, and other personal mobile instruments. As sizes of personal mobile instruments are reduced, the size of the LCD panels used therein has to decrease accordingly. Single chip design is an option to meet the requirement of reduced sizes of personal mobile instruments. In general, only one power voltage (e.g. 3.5 volts) is provided in the single chip, which supports different components that require different levels of voltage. For example, there are various voltage levels used in a single chip TFT (Thin Film Transistor) LCD driver including a system voltage (e.g., 3.3 volts with the symbol of VDD), a source driver voltage (e.g., 5 volts with the symbol of VDDA), gate driver voltages (e.g., −15 volts and 15 volts with the symbols of VGH and VGL), and a common voltage (e.g., varying from −1 volt to 4.5 volts with the symbol of VCOM), which are generated from the power voltage (e.g., 3.5 volts). For modern applications of 3G (or 3.5G) mobile phones and 3.5 inch LCD displays used in automobiles, the power driving capacity designed in the single chip used for a 2.4 inch LCD panel is no longer valid due to larger source driving current and common switching current (for polarity inversion) in modern applications. Thus, the source driving current and common switching current become the bottlenecks of power circuit design and have to be reduced.
FIG. 1 shows a traditional configuration of a source driver 1 and an LCD panel 2. The source driver 1 includes plural source driver outputs 11 (only one source driver output is shown) and a common output amplifier 12. Each source driver output 11 provides a source driver current to a corresponding pixel that is equivalent to a pixel capacitive loading Cs. The common output amplifier 12 provides a common switching current to a common capacitive loading CCOM during line polarity inversion. According to formula (1) below, there are three ways to reduce the current I; that is, to reduce scanning frequency f, to reduce the capacitance C of the capacitive loading, and to reduce the voltage V across the capacitive loading.I=f×C×V  (1)
However, the scanning frequency f is associated with image quality and the capacitance C is associated with the panel size. Thus, these two factors (f and C) are expected to remain unchanged and the only way to reduce the current I is to reduce the voltage V.